It turns out that the HVAC system was was actually rated for something like 200-250 VAC and ran without a hitch on either system. So without ripping everything out and starting over we basically had to support both 208/120 and 240/120. Nobody caught it and there was essentially no documentation so what got installed was a single phase 240/120 generator and a 240 V HVAC system. We were providing emergency power to an IT system and a separate HVAC system. "208" is actually 208/120V and is always coming from a three phase commercial distribution system, whether or not all three phases are used, stemming from the fact that 120V from Hot to Neutral is what most small equipment needs, then 208 is 120 times the square root of 3, for the three phase service, so Hot to Hot is 208V and can work fine on most small equipment that is designed for 240V. You get 120V from Hot to Neutral and 240V from Hot to Hot. The new standard for single phase coming from utilities has been 120/240V for a generation of people now, but old habits die hard. "110/220" is an old standard voltage level that goes back to the days of Edison, but in most places no longer exists other than in the minds of people who don't really know. So in direct response to the question in a way that can make sense to a Liberal Arts major: If they ask how it works, I tell them, all I know is what comes out of the end of the wires.Īll good answers if you are willing to explain single and three phase theory to a non-electrical professional, but in my experience their eyes will glaze over before you get half way through it. It's the modern standard for 3 phase sustems. Besides that, around here it seems to be in the high 190"'s)Ĭ) 120/208 = three hot legs, all 120 to gnd and 208 between any two. If it's truly 120Volts, the high leg is supposed to be 208 volts but to avoid confusing people I avoid using this number. They used it to power those new fangled air cundishers. Around here you will find it in older resi neighborhoods also. Old school commercial system predating the current 120/208 wye system. Two hot legs appx 120 to gnd, one hot leg appx 200 to ground, 240 between any two. Standard residential and small commercial systemī) 120/240 3 phase = Usually referred to here as "3 phase Delta". Todays standard is 120.Ī) 120/240 single phase = two hot legs appx 120 to gnd, 240 between them. Seems to me that in the 60's, 110 was the standard number. 110/115/120 = all the same, different terminology.
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